The present invention relates to an ink jet recording head, an ink jet recording apparatus and a driving method therefor.
In a typical ink jet recording head, an electrothermal transducer is supplied with a driving signal to produce thermal energy to heat ink adjacent the ink generating portion (heater) so as to produce a change of state including bubble creation. The resultant pressure function to eject the ink. To effect this recording, the ink jet recording head comprises the electrothermal transducer (thermal energy generating element), an ink ejection outlet (orifice) and an ink passage (nozzle) communicating with the ejection outlet.
As shown in FIG. 9 the conventional ink passage generally is straight from the ejection outlet to the supply port (rear end or upstream end adjacent the common ink chamber) except the ejection outlet portion, for the purpose of smooth flowing of the ink. However, with such a structure of the ink passage, the pressure produced by the bubble creation due to the power supply to the heater transmits directly toward upstream as well as toward downstream, with respect to the direction of the ink flow (back wave).
The back wave impedes the flow of the refilling ink from the upstream, and therefore, the time required for the refilling is longer. This imposes difficulty to the high speed ink ejections.
Where the recording head has a plurality of ink passages communicating with the upstream common ink chamber, the backwave is influential to other ink passages by way of the common chamber (cross talk). So, there is a problem of instable ejection.
In addition, with the conventional ink passage, the cavitation produced at the time of extinction or collapse of the bubble significantly damages the heater with the result of lower durability, for example, 1xc3x97108 pulses per nozzle.
Japanese Laid-Open Patent Application No. 100169/1979, 40160/1986 and U.S. Pat. No. 4,882,595 propose provision of a flow resistance element at an upstream side of the ejection heater for the purpose of reducing the backwave, the vibration of the meniscus and the cross talk and the improvement in the response property. However, no consideration has been paid to the cavitation, and therefore, the sufficient service life of the heater is not achieved.
Japanese Laid-Open Patent Application No. 138460/1974 which has been assigned to the assignee of this application has proposed a recording head having an ejection outlet facing a heater surface so that the ink is ejected in the direction perpendicular to the direction of the flow of the refilling ink, wherein the ink passage wall is deformed adjacent the heater to shift the position of the bubble upon the collapse thereof to suppress the influence of the cavitation.
In this Japanese Laid-Open Application, the damage to the ink passage wall and the electrode or the like adjacent the heater still remains. Particularly in the case of the recording head wherein the ejection outlet, the heater and the ink supply port of the common chamber are disposed along a line, the ink flows to the heater upon the collapse of the bubble not only from the ink supply port (upstream) but also from the ejection side because of the retraction of the meniscus at the ejection outlet. Therefore, it is difficult to sufficiently shift the bubble collapse position from the heater.
As for the driving method for the ink jet recording head having plural heaters involves a problem that when the plural heaters are simultaneously driven, a large electric current is required, and the ink droplets ejected through the adjacent nozzles interfere with each other to degrade the print quality, as disclosed in Japanese Laid-Open Patent Application No. 109672/1980. In order to solve the problems, it has been proposed that the heaters are divided into plural groups which are driven simultaneously, respectively, thus reducing the number of the heaters simultaneously driven and thus preventing the interference between the ink droplets through the adjacent nozzles.
However, in this conventional structure, when a small number of nozzles are driven simultaneously, the refilling and the restoring of the meniscus are accomplished in a short period. However, when the number of simultaneously driven nozzles is large, they are not accomplished for a short period. In this case, the refilling frequency reduces from 8 KHz-4 KHz, approximately, for example. Usually, the minimum repeatable frequency is selected as the upper limit of the driving frequency of the recording head, and therefore, a high frequency driving, and therefore, a high speed driving is not possible.
Accordingly, it is a principal object of the present invention to provide a recording head and a recording apparatus wherein the meniscus retraction is suppressed.
It is another object of the present invention to provide a recording head and a recording apparatus wherein the backwave is reduced.
It is a further object of the present invention to provide a recording head and a recording apparatus wherein the refilling period can be reduced.
It is a further object of the present invention to provide a recording head and a recording apparatus wherein the cross talk due to the backwave is reduced.
It is a further object of the present invention to provide a recording head and a recording apparatus wherein the collapsing energy of the bubble can reduced, so that the cavitation can be reduced.
It is a further object of the present invention to provide a recording head and a recording apparatus wherein the durability of the heater, electrode and/or ink passage wall can be improved.
It is a further object of the present invention to provide a driving method wherein the nozzles are driven in a time-dividing manner, and the rest periods are properly selected so that the refilling period is reduced, by which the ejection frequency is significantly improved.
In an embodiment of the present invention, the plural heaters are divided into some groups which are driven simultaneously. After the heaters of a certain group is driven (supplied with the electric energy) to create bubbles, the heaters of the next group is supplied with the electric energy within the period from the driving of the former heater to the maximum bubble time. By doing so, the refilling period is reduced, and therefore, the driving frequency can be increased. In addition, the process from the bubble creation to the bubble collapse can be stabilized for the number of nozzles, by which the deviations of the shot positions of the ink droplets can be reduced.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.